This invention relates to a method of making a thin film by evaporation, and more particularly relates to an improved method of making a thin film with uniform thickness by using an evaporation step which is highly practical for mass production of thin film components and devices.
Thin films are used widely for constructing electronic solid state components and devices and the thickness uniformity of such films is an important requirement in mass production. As methods of making thin films, vacuum evaporation, sputtering and vapor phase reaction processes are well known. Such methods, however, have not been capable of providing thin films of satisfactorily uniform thickness.
FIG. 1 is a schematic illustration of a typical conventional vacuum deposition apparatus. In a vacuum chamber 1, a disk of source material 2 and a substrate 3 supported by a holder 4 are placed opposite to each other. Reference numeral 5 represents a deposited thin film. The deposited film 5 exhibits the thickness distribution as shown in FIGS. 2A and 2B. FIG. 2A illustrates a plan view of the film 5 in which contour lines 6 of the thickness are given and FIG. 2B is a graph illustrating the thickness distribution along line I--I of FIG. 2A. As seen from these figures, the thickness decreases from the center of the disc to the periphery. Such non-uniformity of the deposited film is due to the geometric arrangement of the source material 2 and the substrate 3 and is about .+-.10%.
There has been developed a method of compensating for the variation of film thickness dependent upon the location on the substrate, in which a moving mask plate partially interrupts the evaporated source material from depositing onto the substrate, i.e., the interruption rate is varied according to the location on the substrate so as to equalize the deposition rate.
The above method is quite effective, but further improvement has been required for practical use in mass production.